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What's in a CFL?

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carbonzit

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Taking the trash out today, I spotted the base of a broken CFL outside the cans, obviously dropped by a neighbor. Naturally, I took it inside and opened it up. (It looked like a fairly small one, 10-15W max.) Inside, I found:

  • 3 inductors (2 on small bobbins and one looking like a small transformer)
  • 2 Q's, look like MOSFETS (marked "3003LD6", couldn't find any datasheets on them)
  • 11 (!) diodes, not counting one zener
  • 5 resistors
  • bunch of capacitors, including a 22µF 200V electrolytic

Complicated little buggers. (These were all through-hole parts; nothing surface-mount.)

I salvaged the inductors, which can probably be used in one of my projects.

So all this stuff gets landfilled every time someone throws a dead CFL away. (Yeah, I know, they're supposed to be recycled, but we all know this doesn't happen to most of them, and besides, even for those that do get returned to some Official Recycling Station, how much of this electronic stuff do you suppose actually gets reclaimed?)

Oh, and it might interest you to know that the connections to the bulb itself weren't soldered but were wire-wrapped, of all things. My guess is that the power supply is made by one manufacturer, and the bulbs get assembled at a different plant, where they decided it would be faster/cheaper to wire-wrap the connections rather than solder them.

So the next time one of your CFLs goes out, you might want to open it up and check its connections ...
 
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I agree about salvaging the components -- I've gotten inductors from them too.

The typical CFL has on the order of milligrams of mercury in it, so it's a good idea to take them to a recycling center. These recycling centers are free in many cities and it's nice to know you're keeping that crud out of landfills. Now, the mercury from one CFL isn't terribly much, but they're made in quantities of many millions, so that adds up to a fair amount of mercury.

I remember reading a study 30+ years ago that indicated that properly-made wire-wrap joints were extremely good. And you don't get the copper intermetallics causing brittleness that are one cause of solder joint failures. The main downside was bulk and cost of labor.

Oh, and don't toss old GFI outlets -- you can salvage two nice current transformers from them (200:1 and 1000:1).
 
I think those parts you mentioned make up an inverter, but I am not positive. I'm thinking I read somewhere that you can make a really good transformer (flyback, ignition coil, etc.) driver with one of those things. Just another reason to try to salvage them :D
Der Strom
 
What you see is a rectified AC mains with filter cap to create high voltage DC. The HV DC is chopped at high frequency (25kHz to 40kHz) by the two MOSFET's. At this point it is pretty similar to old 50/60 Hz magnetic ballast design except the ballast is operating at high frequency so it can be small in inductance and physical size.

Fluorescent bulbs are more efficient in terms of watts per lumens when driven at 25kHz to 40kHz then at 50/60 Hz.
 
Don't know where you get "inverter": they're small switch-mode power supplies (SMPSs).
To be more precise they are switch-mode ballasts, which act like constant current sources to regulate the current through the fluorescent tube. Fluorescent tubes have a low impedance when operating (not unlike an LED) and require a current source for proper operation.
 
Don't know where you get "inverter": they're small switch-mode power supplies (SMPSs).

Like this (page has dozens more examples).

To be more precise they are switch-mode ballasts, which act like constant current sources to regulate the current through the fluorescent tube. Fluorescent tubes have a low impedance when operating (not unlike an LED) and require a current source for proper operation.

Well, my mistake. I thought I had read somewhere that CFLs had built-in inverters, but perhaps I am thinking of something else.
 
Fluorescent tube have negative resistance slope, unlike LED's. The more current put through a flourescent bulb, the lower their impedance gets, resulting in a lower terminal voltage as current is increased. LED's have positive resistance slope, the more current put through them the higher the terminal voltage across them.

Old 50/60 Hz magnetic ballast also operate as an approximation of a current source, which is basically a high voltage source with a large resistance/reactance in series to limit current. LED's are also operated from an approximate current source.

Most cheap CFL have no feedback mechanism to regulate bulb current, relying solely on voltage in series with fixed reactance to set current through bulb. This causes issues with cold operation. When hot, bulb has lower impedance so series ballast must have enough reactance to prevent too much current causing bulb burn out. When cold, bulb impedance is higher and may not strike (ignite gas) or have lower bulb run current having poor light output until bulb warms up.

The rest of the circuitry shown in the link is to create the 25kHz-40kHz oscillator to drive the MOSFET gate inputs.
 
Well, my mistake. I thought I had read somewhere that CFLs had built-in inverters, but perhaps I am thinking of something else.
Perhaps you were thinking of battery operated fluorescents. They require an inverter to step up the voltage to the tube's operating voltage.
 
The light tube of a fluorescent light is glass. The wires going through the glass are iron (the same expansion with temperature change as glass) so they are difficult to solder and a pain to weld (the wires on incandescent bulbs are welded). So they use wire-wrap.
 
Perhaps you were thinking of battery operated fluorescents. They require an inverter to step up the voltage to the tube's operating voltage.

Hmm, that could very well be. I recently took one of those apart, so maybe it came up in my research about the device :p
 
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